Potassium Rhodinitrite, K₃Rh(NO₂)₆

An acidified solution of rhodium chloride or the double potassium rhodium chloride, containing not more than 5 grams of rhodium per litre, is raised to boiling, and successive small additions of potassium nitrite added until the solution is bleached and a slight turbidity is produced. On cooling, the anhydrous Potassium Rhodinitrite, Potassium Rhodium Nitrite, K₃Rh(NO₂)₆ or 3KNO₂.Rh(NO₂)₃, crystallises out, and may be dried at 105° C. The crystals are white, almost insoluble in cold water, quite insoluble in alcohol. On warming with concentrated hydrochloric acid it yields potassium hexa- chlor-rhodite, K₃RhCl₆.3H₂O. The insolubility of potassium rhodium nitrite may be made use of in the preparation of pure rhodium, as well as for its quantitative estimation. When heated to incipient redness until evolution of gas ceases, the product, K₂O.6RhO₂, is obtained.